1. Field of the Invention
The present invention relates to a signal generator, a test apparatus and a circuit device. The present invention particularly relates to a signal generator that can freely correct the waveform of an output signal.
2. Related Art
A typical method of testing a device under test (DUT) such as a semiconductor circuit is to input a predetermined signal into the DUT, and measure an output signal from the DUT to judge whether the DUT is good or bad. For example, the signal input into the DUT has a predetermined logical pattern, and the output signal from the DUT is judged whether to have a logical pattern matching an expected value pattern so as to determine whether the DUT operates normally or not.
According to the above-described testing method, the test apparatus inputs the predetermined signal into the DUT. Here, this signal may attenuate while being transmitted on the path from the test apparatus to the DUT. If such attenuation occurs, the signal input into the DUT may have a different logical pattern from a logical pattern that is designated to be input into the DUT.
To solve this problem, the typical test apparatus has a function to correct the waveform of the test signal in advance based on the potential signal attenuation on the transmission path. For example, the test apparatus generates a plurality of pulse signals having different pulse widths based on the timing of the edge of the test signal, and adds the waveforms of these pulse signals to the waveform of the test signal. Thus, the test apparatus sharpens the edge portion of the test signal (see unexamined Japanese Patent Application Publication No. 2002-40112, for example).
Here, such a typical test apparatus can sharpen the edge of the test signal, but can not freely correct the waveform of the test signal. To be specific, since the test apparatus corrects the test signal by adding the pulse widths of the pulse signals generated based on the timing of the edge of the test signal, the test apparatus can not make a correction to compensate a reflected wave and the like which may occur in a phase that is temporally distant from the edge, for example. In addition, the typical test apparatus can sharpen the edge, but can not blunt the edge.
For the reasons stated above, the typical test apparatus can not always test the DUT accurately. Furthermore, it has not been possible to test quantitatively a waveform equalizing function of the DUT when the device has a function of restoring an attenuated test signal, that is to say, a waveform equalizing circuit.